In semiconductor manufacture, extremely small electronic devices are formed in separate dies on a thin, flat semiconductor wafer. In general, various materials which are either conductive, insulating, or semiconducting are utilized to form a semiconductor wafer. These materials are patterned, doped with impurities, or deposited in layers by various processes to form the integrated circuits. A completed device is referred to as a semiconductor.
One process that is utilized in the manufacture of semiconductors is referred to as chemical mechanical planarization (CMP). In general, chemical mechanical planarization involves holding or rotating a thin, flat wafer of semiconductor material against a wetted polishing surface under controlled chemical, pressure, and temperature conditions. A chemical slurry containing a polishing agent such as alumina or silica is utilized as the abrasive medium. Additionally, the chemical slurry may contain chemical etches for etching various surfaces of the wafer.
In general, a semiconductor wafer is subjected to chemical mechanical planarization to remove topography, layers of material, surface defects such as crystal lattice damage, scratches, roughness, or embedded particles of dirt or dust. This process is utilized in the formation of various integrated circuit devices of a semiconductor and to improve the quality and reliability of a semiconductor.
In the mechanical planarization process, a rotating polishing head is typically utilized to hold the wafer under controlled pressure against a rotating polishing platen. The polishing platen is typically covered with a relatively soft, wetted material such as blown polyurethane. The chemical slurry is metered onto the polishing platen and is selected to provide an abrasive medium and chemical activity for the etching.
Such apparatus for polishing thin, flat semiconductor wafers are well known in the art. U.S. Pat. Nos. 4,193,226 and 4,811,522 to Gill, Jr. and U.S. Pat. No. 3,841,031 to Walsh, for instance, disclose such apparatus. Another such apparatus is manufactured by Westech Engineering and designated as a Model 372 Polisher.
A particular problem encountered in the use of such chemical mechanical polishing apparatus is in the determination that a part has been planed to a desired planar endpoint. It is often desirable, for example, to remove a thickness of oxide material which has been deposited onto a substrate, and on which a variety of integrated circuit devices have been formed. In removing or planarizing this oxide, it is desirable to remove the oxide to the top of the various integrated circuit devices without removing any portion of a device.
In the past, this planarization process has been accomplished by control of the rotational speed, downward pressure, chemical slurry, and time of the planarization process. The planar endpoint of a planarized surface has been detected by mechanically removing the semiconductor wafer from the planarization apparatus and physically measuring the semiconductor wafer by techniques which ascertain dimensional and planar characteristics. If the semiconductor wafer does not meet specification, it must be loaded back into the planarization apparatus and planarized again. Alternately, an excess of material may have been removed from the semiconductor wafer rendering the part as substandard.
In general, however, there has been no provision in the art for in situ endpoint detection of a planarized surface during the planarization process. The present invention is directed to a novel method and apparatus for in situ endpoint detection of a planarized surface during the mechanical planarization process.